1. Field of the Invention
The invention relates to a trench gate type transistor and a method of manufacturing the same.
2. Description of the Related Art
A DMOS transistor is a double-diffused MOS field effect transistor and used as a power semiconductor device for a power supply circuit, a driver circuit or the like. A trench gate type transistor is known as a type of DMOS transistor.
This trench gate type transistor is configured by forming a gate oxide film 215 in a trench 214 formed in a semiconductor layer 212 and forming a gate electrode 216 covering the gate oxide film 215 in the trench 214 as shown in FIG. 48. A body layer and a source layer (not shown) are further formed in the front surface of the semiconductor layer 212 on the sidewall of the trench 214 by double-diffusion in the vertical direction.
A trench gate type transistor is described in Japanese Patent Application Publication Nos. 2005-322949 and 2003-188379.
As shown in FIG. 48, however, at a portion 216S where the gate electrode 216 is led from inside the trench 214 to the outside (hereafter, referred to as a leading portion), there is a problem that leakage current (hereafter, referred to as gate leakage current) occurs between the gate electrode 216 and the semiconductor layer 212. According to the examination by the inventors, this is firstly because the gate oxide film 215 is thin, and secondly because a corner portion 212C of the semiconductor layer 212 faces the gate electrode 216 at the leading portion 2165 with the thin gate oxide film 215 being therebetween and thus electric field concentration occurs in this portion.